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  • 1
    Online Resource
    Online Resource
    Berlin [u.a.] : Springer
    Part of " Lecture notes in physics"
    Keywords: Sternatmosphäre ; Konvektion ; Sternmodell ; Konvektion ; Stellare Konvektion ; Konferenzschrift 1976 ; Sternatmosphäre ; Konvektion ; Sternmodell ; Konvektion ; Stellare Konvektion
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource
    ISBN: 9783540085324
    Series Statement: Lecture notes in physics 71
    Language: English
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  • 2
    Online Resource
    Online Resource
    Berlin [u.a.] : Springer
    Part of " Lecture notes in physics"
    Keywords: Sterninneres ; Sternrotation ; Turbulente Strömung ; Mischen ; Sternaufbau ; Festschrift ; Konferenzschrift 1989 ; Sterninneres ; Sternrotation ; Turbulente Strömung ; Mischen ; Sternaufbau
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource
    ISBN: 9783540530596 , 9783540463979
    Series Statement: Lecture notes in physics 366
    Language: English
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 82 (1983), S. 387-400 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Preliminary solar envelope models have been computed using the single-mode anelastic equations as a description of turbulent convection. This approach provides estimates for the variation with depth of the largest convective cellular flows, akin to giant cells, with horizontal sizes comparable to the total depth of the convection zone. These modal nonlinear treatments are capable of describing compressible motions occurring over many density scale heights. Single-mode anelastic solutions have been constructed for a solar envelope whose mean stratification is nearly adiabatic over most of its vertical extent because of the enthalpy (or convective) flux explicitly carried by the big cell; a sub-grid scale representation of turbulent heat transport is incorporated into the treatment near the surface. The single-mode equations admit two solutions for the same horizontal wavelength, and these are distinguished by the sense of the vertical velocity at the center of the three-dimensional cell. It is striking that the upward directed flows experience large pressure effects when they penetrate into regions where the vertical scale height has become small compared to their horizontal scale. The fluctuating pressure can modify the density fluctuations so that the sense of the buoyancy force is changed, with buoyancy braking actually achieved near the top of the convection zone. The pressure and buoyancy work in the shallow but unstable H+ and He+ ionization regions can serve to decelerate the vertical motions and deflect them laterally, leading to strong horizontal shearing motions. It appears that such dynamical processes may explain why the amplitudes of flows related to the largest scales of convection are so feeble in the solar atmosphere.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 265 (1999), S. 501-505 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Broad Absorption Lines (BALs) prove the existence of a high velocity outflowing gas with metallicities larger than solar in the central few parsecs of high redshift quasars. At the same distance from the black hole, accretion disks in quasars and Active Galactic Nuclei (AGN) are locally gravitationally unstable, and clumps must form with a size of the order of the scale height of the disk. This is hardly a coincidence, and we have tried to link these two facts. We have assumed that the unstable clumps give rise to protostars, which become massive stars after a rapid stage of accretion, and explode as supernovae, producing strong outflows perpendicular to the disk and inducing outward transfer of angular momentum in the plane of the disk. As a consequence a self-regulated disk made of gas and stars where supernovae sustain the inflow mass rate required by the AGN is a viable solution in this region of the disk. This model could explain the BALs, and could also account for a pregalactic enrichment of the intergalactic medium and of the Galaxy, if massive black holes formed early in the Universe.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 85 (1998), S. 79-90 
    ISSN: 1572-9672
    Keywords: Stellar interiors ; stellar rotation ; turbulent transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract While the solar convection zone is very well mixed by its turbulent motions, chemical composition gradients build up in the radiative interior due to microscopic diffusion and settling, and to nuclear burning. Standard models, which ignore any type of macroscopic transport, cannot explain the depletion of lithium in solar-type stars, as they evolve; neither do they account for the observed profile of molecular weight at the base of the solar convection zone. Such macroscopic transport can be achieved through thermally driven meridian currents, through turbulent diffusion generated by differential rotation and possibly through gravity waves. These processes transport also angular momentum, and therefore the internal rotation profile of the Sun provides a crucial test for their relative importance. So does also the behavior of tidally locked binaries, which appear to destroy less lithium than single stars of the same mass.
    Type of Medium: Electronic Resource
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